Re: [PATCH v2] crypto: AF_ALG - limit mask and type

From: Herbert Xu
Date: Fri Dec 22 2017 - 02:36:31 EST

On Tue, Dec 19, 2017 at 07:25:04AM +0100, Stephan Müller wrote:
> The user space interface allows specifying the type and the mask field
> used to allocate the cipher. As user space can precisely select the
> desired cipher by using either the name or the driver name, additional
> selection options for cipher are not considered necessary and relevant
> for user space.
> This fixes a bug where user space is able to cause one cipher to be
> registered multiple times potentially exhausting kernel memory.
> Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx>

This will break users of CRYPTO_ALG_KERN_DRIVER_ONLY. I think
we should add CRYPTO_ALG_TESTED to the blacklist since there is
no sane reason to use it here.

Most other problems however would be bugs in the template code.
The first thing a template does when it creates an instance is
to check whether the resulting algorithm would fulfil the requested
type/mask using crypto_check_attr_type. So if that's not working
then we should fix it there as it may also be triggered via other
code paths that can create instances.

Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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